The present invention relates to a suction system for an internal combustion engine.
It is preferable that suction passages for an internal combustion engine for an automotive vehicle meet the following conditions: excellent intake efficiency in a wide range of rotation ranging from low speed to high speed and, for a multiple cylinder engine, uniform distribution of air and mixture among cylinders.
Referring to FIG. 11, there is shown a previously proposed suction system for a V-type opposed six cylinder engine which is disclosed, for example, in JP-A 60-69255.
As shown in FIG. 11, there are arranged two aggregate portions or surge tanks 75, 76 for aggregating branch pipes 73, 74 which communicate with cylinders of left and right banks 71, 72. The two aggregate portions 75, 76 are disposed in parallel with a crankshaft, each having an end at which a throttle valve 77 is mounted.
With such a known suction system, however, since the throttle valve 77 is mounted at the end of each aggregate portion 75, 76, the suction passages connecting the throttle valve 77 and the intake valves of the cylinders have different lengths, resulting in a dispersion of the intake efficiency of the cylinders in a range of low speed rotation in which resonance supercharging is carried out.
Further, since the aggregate portions 75, 76 are disposed on center lines of the banks 71, 72, respectively, ignition plugs also disposed on the center lines of the banks 71, 72 cannot be mounted and detached without removing the suction system from an engine main body. Furthermore, due to the above construction, there is a design restriction in that an engine hood line of the vehicle has a center portion higher than a side portion.
It is, therefore, an object of the present invention to provide a suction system for an internal combustion engine which contributes to an increase in the intake efficiency with a restricted overall height of the engine.